The present invention relates to private base stations arranged to provide communication directly between a cellular mobile telephone, operable within in a macro cellular network, and a public switched terrestrial network.
In cellular networks, it is necessary to adopt an optimized coverage policy in terms of providing sufficient signal strengths at locations within the region covered while minimizing infrastructure expenditure. Experience has shown that user penetration is price sensitive and customers will tolerate a degree of signal degradation when the level of service is reflected in their connection charges. Thus, it is theoretically possible to provide superb radio coverage over wide geographical areas, however the cost of doing this often proves prohibitive and would result in a reduced customer penetration with system operators being unable to establish a profitable network.
In areas where it is not possible to obtain a sufficiently strong communication signal, other modes of communication, such as connection to a public switched telephone network are often available. Furthermore, customers may be reluctant to use mobile equipment if less expensive land based systems are readily accessible at a particular location. This will tend to discourage customers from regularly using mobile equipment which in turn may reduce overall system use due to the mobile equipment not being readily accessible.
A private base station provides a mechanism for relieving the above problems in that, in preference to being connected to an established cellular network, a mobile phone user may establish a connection to a dedicated private base station which in turn allows the mobile telephone equipment to be used to establish conventional telephone calls via land based networks such as the PSTN. Thus, when the customer is in close proximity to their private base station, it is possible for the customer to obtain the benefits of using a personal mobile telephone while at the same time only experiencing connection costs equivalent to those experienced when using a PSTN handset.
Two significant problems exist with the use of conventional base station equipment in the role of a private base station. Firstly, the private base station must facilitate communication with mobile telephones in its geographical area while at the same time it is essential that it does not interfere with surrounding cellular networks. Secondly, existing base stations are configured to communicate with a plurality of users therefore although the cost of an individual base station is relatively high, this cost, over a period of time, is shared by many users as they enter the geographical area. However, private base stations will tend to provide services for one user or at most a relatively small number of users therefore the overall cost of providing such a base station must be substantially reduced if it is to appear commercially attractive to potential users.
A conventional base station is disclosed in British patent publication 2 249 922, wherein communication between a cellular mobile telephone and a public switch terrestrial network is provided, while minimising interference with similar base stations. Base stations for both public and private use are also disclosed in International patent publication 92/04796.
According to a first aspect of the present invention, there if provided a private base station arranged to provide communication directly between a cellular mobile telephone, operable within a macro cellular network, and a public switched terrestrial network; wherein said base station includes processing means configurable to transmit signalling information over an available time slot to establish a call; and said processing means is configurable to transmit user-traffic via said available time slot after a call has been established, thereby minimising interference with similar base stations.
In a preferred embodiment, the processing means is configured to synchronise said base station to a second base station and thereafter identify itself as being available to synchronise a third base station.
According to a second aspect of the present invention, there is afforded a method of providing direct communication between a cellular mobile telephone, operable within a macro cellular network, and a public switched terrestrial network, by means of a private base station including processing means, comprising steps executed by said processing means of transmitting signalling information over an available time slot to establish a call; and transmitting user traffic via said available time slot after a call has been established, thereby minimising interference with similar base stations.